Seasonal and synoptic scale circulation linked to dry spring conditions in Brazil

Brazilian spring (SON) of 2023 was marked by the occurrence of heatwaves and droughts in the tropics as well as extreme daily rainfall produced by a series of extratropical cyclones in subtropical latitudes. These events were (partially) attributed to a persistent ridge over western subtropical South Atlantic which blocked the propagation of extratropical disturbances further equatorward over Brazil. El Niño conditions further intensified the tropical subsidence, contributing to the tropical drought. Here, we assess whether this combination of extreme events was just only a coincidence or could be attributed to a new emerging trend. We compared two periods (1979-1993 and 2009-2024) using ERA5 upper-level (300hPa) circulation during austral spring (SON), we identify a strengthening of the polar jet over South Pacific and the weakening (strengthening) of the subtropical jet over South Pacific (South America) that favours (hinders) the propagation of synoptic-scale  (planetary scale) RW towards subtropical South America. We evaluate the extent to which some of these changes  may emerge from the displacement and change of intensity of the tropical and subtropical convection, which is the dominant diabatic control on the intensity and location of the Rossby Wave Sources over the (sub)tropical Pacific. Finally, we evaluate the connection between the seasonal changes in large-scale circulation and the synoptic-scale events throught changes in the activity of Rossby Wave Packets (RWPs) and Rossby Wave Breaking (RWB) events over the region. These provisional results provide insight about changes in the interaction between diabatic forcing, Rossby waves, and synoptic-scale circulation contributing to compound extreme events like those observed over South America in 2023.